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We occasionaly hit following assert failure in 'perf top', when processing the
/proc info in multiple threads.
perf: ...include/linux/refcount.h:109: refcount_inc:
Assertion `!(!refcount_inc_not_zero(r))' failed.
The gdb backtrace looks like this:
[Switching to Thread 0x7ffff11ba700 (LWP 13749)]
0x00007ffff50839fb in raise () from /lib64/libc.so.6
(gdb)
#0 0x00007ffff50839fb in raise () from /lib64/libc.so.6
#1 0x00007ffff5085800 in abort () from /lib64/libc.so.6
#2 0x00007ffff507c0da in __assert_fail_base () from /lib64/libc.so.6
#3 0x00007ffff507c152 in __assert_fail () from /lib64/libc.so.6
#4 0x0000000000535373 in refcount_inc (r=0x7fffdc009be0)
at ...include/linux/refcount.h:109
#5 0x00000000005354f1 in comm_str__get (cs=0x7fffdc009bc0)
at util/comm.c:24
#6 0x00000000005356bd in __comm_str__findnew (str=0x7fffd000b260 ":2",
root=0xbed5c0 <comm_str_root>) at util/comm.c:72
#7 0x000000000053579e in comm_str__findnew (str=0x7fffd000b260 ":2",
root=0xbed5c0 <comm_str_root>) at util/comm.c:95
#8 0x000000000053582e in comm__new (str=0x7fffd000b260 ":2",
timestamp=0, exec=false) at util/comm.c:111
#9 0x00000000005363bc in thread__new (pid=2, tid=2) at util/thread.c:57
#10 0x0000000000523da0 in ____machine__findnew_thread (machine=0xbfde38,
threads=0xbfdf28, pid=2, tid=2, create=true) at util/machine.c:457
#11 0x0000000000523eb4 in __machine__findnew_thread (machine=0xbfde38,
...
The failing assertion is this one:
REFCOUNT_WARN(!refcount_inc_not_zero(r), ...
The problem is that we keep global comm_str_root list, which
is accessed by multiple threads during the 'perf top' startup
and following 2 paths can race:
thread 1:
...
thread__new
comm__new
comm_str__findnew
down_write(&comm_str_lock);
__comm_str__findnew
comm_str__get
thread 2:
...
comm__override or comm__free
comm_str__put
refcount_dec_and_test
down_write(&comm_str_lock);
rb_erase(&cs->rb_node, &comm_str_root);
Because thread 2 first decrements the refcnt and only after then it removes the
struct comm_str from the list, the thread 1 can find this object on the list
with refcnt equls to 0 and hit the assert.
This patch fixes the thread 1 __comm_str__findnew path, by ignoring objects
that already dropped the refcnt to 0. For the rest of the objects we take the
refcnt before comparing its name and release it afterwards with comm_str__put,
which can also release the object completely.
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Lukasz Odzioba <lukasz.odzioba@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Wang Nan <wangnan0@huawei.com>
Cc: kernel-team@lge.com
Link: http://lkml.kernel.org/r/20180720101740.GA27176@krava
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.